1. Field of the Invention
The invention relates to motor vehicles, and more particularly to a drive train arrangement for a motor vehicle driven by an internal combustion engine.
2. Description of the Related Art
In the torque transmission path of conventional drive train arrangements for motor vehicles, a friction-gearshift clutch is arranged between the internal combustion engine and a speed-change gear, which may be a multi-speed, manually-shifted gear. To start the vehicle or change the speeds of the speed-change gear, the driver engages and disengages the friction-gearshift clutch by means of a clutch pedal. To automate the gearshift clutch, an actuator can be provided instead of the clutch pedal.
The transmission capacity of the friction-gearshift clutch (i.e., the amount of torque capable of being transmitted by the clutch) depends primarily on the pressure force of the clutch main spring and the coefficient of friction of the friction lining material of the clutch disk. The transmission capacity can be subject to temperature-dependent fluctuations (fading). In order to ensure that the gearshift clutch reliably transmits the torque for which it has been designed, even under favorable operating conditions (e.g., when the coefficient of friction of the friction lining is relatively low), relatively high transmission reliability has been required. The transmission reliability is the ratio of the slip moment of the gearshift clutch when the clutch is exercising its maximum pressure force on the friction linings to the maximum engine torque. The slip moment at maximum pressure force is the product of the maximum pressure force exerted by the gearshift clutch (i.e., its pressure plate) on the friction linings multiplied by the coefficient of friction of the friction linings multiplied by the mean friction radius multiplied by the number of friction surfaces. In conventional gearshift clutches, the nominal transmission reliability, based on a coefficient of friction of 0.25, is approximately 1.3 to 1.5. However, the effective transmission reliability is approximately 2.3 to 2.5, since the effective or actual coefficient of friction during normal driving is approximately 0.4.
Because conventional friction-gearshift clutches are designed for very high effective transmission reliability, the entire drive train of the motor vehicle is heavily stressed during dynamic processes, e.g. during abrupt clutch engagement or while undergoing rotary vibration resonances. For this reason, not only the components of the gearshift clutch, but also the other parts of the drive train, must be of sturdy design so as to be able to tolerate even the rarely reached torque limit values. The trend toward higher engine torques also makes necessary higher pressure forces of the diaphragm spring, which usually serves as the clutch main spring. Moreover, the useful life of such strong diaphragm springs must also be taken into account. Finally, the requirement for high transmission reliability (and thus high spring forces of the clutch main spring) results in high activation forces in the clutch disengagement system, so that the components arranged in the power flow of the clutch disengagement system are also more strongly loaded and thus must also be sturdily designed.